I had to register to get into this thread. It seems that a lot of people (maybe I'm wrong) think that a sight or scope is simply zeroed at a certain distance and the bullet follows a straight line to that path and then starts to sink. I wish this were the case, because things would be a lot easier. The truth is the bullet starts to drop right after it leaves the barrel.
Here's a web page I found that explains bullet trajectory:
http://www.absoluteastronomy.com/topics/Rifleman%27s_rule
If you look at the third picture with the rifle and the bullet trajectory you'll notice that the rifle is zeroed in two different points because of the bullet trajectory. I think, I may be wrong, that a M-16 that is zeroed at 300m will also be zeroed at 100m because the bullet is shot upward to cross the sights at 100m, raises up on an arch then comes down to cross the sights again at 300m.
When I was in the army we sighted our weapons for 300m and you had to adjust your aiming to be able to hit the target any closer than 300m or any further than 300m (we didn't shoot any further than 300m). IRL you have to know the bullet trajectory in order to aim correctly. I remember when shooting at a 150m target IRL I had to shoot it at the waist line in order to hit center mass.
I guess this all doesn't really matter, but it's interesting to learn something new. I hope no one already covered this in the thread.
